1:1 or 1:2 solid stoichiometric adducts of TiCl₄ with anthraquinone‐1,4, anthraquinone‐1,2, naphtacenequinone‐5,12, pentacenequinone‐6,13 have been prepared. The very important lowering Δω(C=O) of the respective IR. carbonyl frequencies, ranging from −160 to −100 cm⁻¹, shows that the acceptor is linked by a dative bond to the carbonyl oxygen atom acting as donor. On the basis of calculations and various considerations, the reduction of the C=O double bond character is confirmed. Linear relations are found to exist between the oxydo‐reduction or the polarographic reduction potential of the quinones, and their antisymetric ω_a (C=O) frequencies, the values of Δω, and the O → Ti vibrations, respectively.